How is nozzle pressure used in calculating PDP for a given attack line?

How is nozzle pressure used in calculating PDP for a given attack line?

• A. PDP = nozzle pressure - friction loss - elevation head
• B. PDP = nozzle pressure + friction loss + elevation head
• C. PDP = nozzle pressure x friction loss x elevation head
• D. PDP = nozzle pressure only

Answer: (B)

When sizing the pump discharge pressure for an attack line, you must deliver enough pressure to the nozzle to meet its required operating pressure after losses along the hose and any elevation change. The nozzle requires a specific pressure to achieve the desired flow and spray, but as water moves through hose, friction losses reduce pressure, and if the nozzle is higher than the pump, elevation adds head that must be overcome. So you add these components together to get the pump discharge pressure: nozzle pressure plus friction loss plus elevation head. For example, if the nozzle needs 100 psi, the hose line loses 25 psi to friction, and the elevation difference adds 10 psi, the PDP would be 135 psi. Subtracting or multiplying would misrepresent how pressure actually drops along the line, and relying on nozzle pressure alone ignores the losses and elevation that must be overcome.

When sizing the pump discharge pressure for an attack line, you must deliver enough pressure to the nozzle to meet its required operating pressure after losses along the hose and any elevation change. The nozzle requires a specific pressure to achieve the desired flow and spray, but as water moves through hose, friction losses reduce pressure, and if the nozzle is higher than the pump, elevation adds head that must be overcome. So you add these components together to get the pump discharge pressure: nozzle pressure plus friction loss plus elevation head. For example, if the nozzle needs 100 psi, the hose line loses 25 psi to friction, and the elevation difference adds 10 psi, the PDP would be 135 psi. Subtracting or multiplying would misrepresent how pressure actually drops along the line, and relying on nozzle pressure alone ignores the losses and elevation that must be overcome.